Modbus is a master/slave communications protocol where the master initiates transactions and the slave(s) responds with the requested information or action.

Your device can function as a Modbus slave or Modbus master, depending on how it is configured. Your device comes with Modbus slave functionality configured and ready to use. You can add custom Modbus information to the default Modbus slave data provided by your device.

Key terms

Term Definition

Modbus gateway

A communications method that lets you communicate through an Ethernet gateway device to a Modbus serial network connected to that device.

Modbus master

A device that issues commands and receives responses from Modbus slave devices. Serial Modbus networks can only have one Modbus master per network.

Modbus RTU

Serial Modbus protocol format; Modbus RTU transmits data using binary. Master and slave devices must use the same format.

Modbus register/address

Identifies the data to read/write. Modbus register maps are available for Modbus slave devices and detail the information available from the slave device. More than one register may be used to store a single value.

Modbus slave

A device that responds to Modbus commands and performs actions or provides information back to the Modbus master. Most Modbus networks contain multiple slave devices.

Modbus TCP

The Ethernet Modbus protocol format.

Modbus unit ID

The identifier for a slave Modbus device.

You can download your device’s Modbus map from www.se.com and get additional information about the Modbus protocol from www.modbus.org.

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